Truck with a hand-operatable bed

Abstract

This invention discloses a truck with a hand-operatable bed of which the front side under surface is provided with a pair of front wheels and of which the rear side under surface is supported by a hydraulic cylinder, for lifting or lowering the bed, mounted on a pair of rear wheels by means of bearings, which is characterized by being further provided with an overload-sensing device and an alarm-raising device to be put into operation according to the sensing of the overload-sensing device. Because operators can be told about an overload immediately by the devices, they do not have to keep a plunge pump working without being aware of an overload applied on the cylinder as did before. What is more, as they can realize whether the cause of not feeding oil to the cylinder has come from troubles in pressure lines or an overload, they can take measures against the cause at their earliest possible, with the result that the safety and the operatability in handling the truck are improved greatly.

What is claimed is: 
     
       1. A truck with a hand-operatable bed of which the front side under surface is provided with a pair of front wheels, the rear side under surface is supported by a hydraulic cylinder for lifting or lowering said bed, mounted on a pair of rear wheels by means of bearings, a hydraulic fluid reservoir, an overload-sensing device and an alarm-raising device, comprising: a chamber;   a pressure relief valve for venting hydraulic fluid from said hydraulic cylinder into said chamber;   an adjustable bias setting spring for controlling the differential pressure point between said hydraulic cylinder and said chamber at which said pressure relief valve opens;   a bore connecting said chamber to said hydraulic fluid reservoir;   a rod including a first end which is positioned in said bore;   said rod first end including a segment dimensioned to fill said bore and prevent fluid flow from said chamber into said hydraulic reservoir;   a rod bias spring for holding said rod first end segment in said bore;   rod support means for supporting said rod so that a second end of said rod is exposed to ambient pressure and said rod can slide relative to said rod support means;   said rod bias spring having a biasing capacity relative to said adjustable bias setting spring for permitting the pressure increase in said chamber relative to ambient pressure created by said pressure relief valve opening to unseat said rod to permit hydraulic fluid to pass from said chamber into said reservoir; and   electrical switch means positioned in alignment with said second end of said rod and positioned therefrom by a distance which is traversed by said rod when unseated for changing the state of said electrical switch for activating said alarm-raising device.   
     
     
       2. A truck as defined in claim 1, comprising: a piston in said hydraulic cylinder responsive to pressurized hydraulic fluid for raising said truck bed;   a pump for pressurizing hydraulic fluid and causing said fluid to be transported from said hydraulic fluid reservoir to said hydraulic cylinder; and   valve means for controlling the transfer of hydraulic fluid via fluid couplings from said pump to said hydraulic cylinder in a first position and from said hydraulic cylinder to said hydraulic fluid reservoir in a second position.   
     
     
       3. A truck as defined in claim 2 wherein said valve means includes a neutral position for closing the fluid couplings between said hydraulic cylinder and said pump, and said hydraulic cylinder and said hydraulic fluid reservoir. 
     
     
       4. A truck as defined in claim 3, further comprising: a handle for manually operating said hydraulic pump and moving and steering said truck; and   a control means in said handle for mutually exclusively placing said valve means in said first, second or neutral positions.   
     
     
       5. A truck as defined in claim 3, further including a chain for flexibly coupling said control means to said valve wherein said handle may be operated as a pump handle or steering means without interfering with the operation of said control valve. 
     
     
       6. A hand operated hydraulic lift truck, a load, including a hydraulic fluid reservoir, a hydraulic cylinder, an overload-sensing means and an overload alarm means activated when said overload-sensing means senses an overload, comprising: a chamber;   a pressure relief valve for venting hydraulic fluid from said hydraulic cylinder into said chamber;   an adjustable bias setting spring for controlling the differential pressure point between said hydraulic cylinder and said chamber at which said pressure relief valve opens;   a bore connecting said chamber to said hydraulic fluid reservoir;   a rod including a first end which is positioned in said bore;   said rod first end including a segment dimensioned to fill said bore and prevent fluid flow from said chamber into said hydraulic reservoir;   a rod bias spring for holding said rod first end segment in said bore;   rod support means for supporting said rod so that a second end of said rod is exposed to ambient pressure and said rod can slide relative to said rod support means;   said rod bias spring having a biasing capacity relative to said adjustable bias setting spring for permitting the pressure increase in said chamber relative to ambient pressure created by said pressure relief valve opening to unseat said rod to permit hydraulic fluid to pass from said chamber into said reservoir; and   electrical switch means positioned in alignment with said second end of said rod and positioned therefrom by a distance which is traversed by said rod when unseated for changing the state of said electrical switch for activating said overload alarm means.   
     
     
       7. A truck as defined in claim 6, wherein said hydraulic means includes: said hydraulic cylinder;   a piston in said hydraulic cylinder responsive to pressurized hydraulic fluid for raising said load;   a pump for pressurizing hydraulic fluid and causing said fluid to be transported from said hydraulic fluid reservoir to said hydraulic cylinder; and   control valve means for controlling the transfer of hydraulic fluid via fluid couplings from said pump to said hydraulic cylinder in a first position and from said hydraulic cylinder to said hydraulic fluid reservoir in a second position.   
     
     
       8. A truck as defined in claim 7 wherein said valve means includes a neutral position for closing the fluid couplings between said hydraulic cylinder and said pump, and said hydraulic cylinder and said hydraulic fluid reservoir. 
     
     
       9. A truck as defined in claim 8, further comprising: a handle for manually operating said hydraulic pump and moving and steering said truck; and   a control means in said handle for mutually exclusively placing said valve means in said first, second or neutral positions.   
     
     
       10. A truck as defined in claim 9, further including a chain for flexibly coupling said control means to said control valve wherein said handle may be operated as a pump handle or steering means without interfering with the operation of said control valve. 
     
     
       11. A hand-operated hydraulic lift truck including a hydraulic means for lifting or lowering a load, including a hydraulic fluid reservoir, a hydraulic cylinder, an overload-sensing means, and an overload alarm means activated when said overload-sensing means senses and overload, comprising: a pressure relief valve for venting hydraulic fluid from said hydraulic cylinder into said hydraulic fluid reservoir;   an adjustable bias setting spring for controlling the pressure differential pressure between said hydraulic cylinder and said hydraulic fluid reservoir at which said pressure relief valve opens;   a fluid conduit connecting said hydraulic cylinder to said pressure relief valve;   a rod including a first end which is positioned in said fluid conduit;   a rod bias spring for holding said rod first end a controlled distance into said fluid conduit;   rod support means for supporting said rod so that a second end of said rod is exposed to ambient pressure and said rod can slide relative to said rod support means;   said rod bias spring having a biasing capacity relative to said adjustable bias setting spring for permitting a pressure increase in said hydraulic cylinder relative to ambient pressure to displace said rod within said rod support means; and   electrical switch means positioned in alignment with said second end of said rod and positioned therefrom by a distance which is traversed by said rod when displaced for changing the state of said electrical switch for activating said alarm-raising device.   
     
     
       12. A truck as defined in claim 11, wherein said hydraulic means includes: said hydraulic cylinder;   a piston in said hydraulic cylinder responsive to pressurized hydraulic fluid for raising said load;   a pump for pressurizing hydraulic fluid and causing said fluid to be transported from said hydraulic fluid reservoir to said hydraulic cylinder; and   valve means for controlling the transfer of hydraulic fluid via fluid couplings from said pump to said hydraulic cylinder in a first position and from said hydraulic cylinder to said hydraulic fluid reservoir in a second position.   
     
     
       13. A truck as defined in claim 12 wherein said valve means includes a neutral position for closing the fluid couplings between said hydraulic cylinder and said pump, and said hydraulic cylinder and said hydraulic fluid reservoir. 
     
     
       14. A truck as defined in claim 13, further comprising: a handle for manually operating said hydraulic pump and moving and steering said truck; and   a control means in said handle for mutually exclusively placing said valve means in said first, second or neutral positions.   
     
     
       15. A truck as defined in claim 14, further including a chain for flexibly coupling said control means to said valve wherein said handle may be operated as a pump handle or steering means without interfering with the operation of said control valve.